36 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 120 
ative numbers of A and B males should also be noted since they con- 
flict with the alternative that only one of the two males is conspecific 
with the female. If we assume that the two males are not conspecific 
and that the probable sex ratio approaches 1:1, to account for the 
quantitative data on hand requires an additional complicating assump- 
tion, namely, that there are two kinds of females that are morpholog- 
ically indistinguishable (i.e., in the characters that have been exam- 
ined). The two species alternative would have to provide for the 
co-occurrence of the two species over the same limited geographical 
range, when as arule closely related species of Labidocera do not over- 
lap extensively (Fleminger, unpubl.). Thus, this line of reasoning 
becomes burdensome without necessarily contributing to a better 
understanding of the extant data. 
Assuming the diandra population as described above is conspecific, 
three facts stand in evidence that the dimorphism is under relatively 
simple and direct genetic control, namely: (1) dimorphism occurs 
throughout the range; (2) there is no intergrading of dimorphic char- 
acters; and (3) dimorphism is sex linked. These three points also pre- 
vail in the case of Pontella meadii referred to in the preceding section. 
One hypothesis can account for both the basic features and vari- 
ability of the unusual sex ratio in adults and the polymorphism in 
males. It requires the following assumptions: that the male is the 
heterogametic sex, that the gene (or polygene) controlling morph type 
is on the X chromosome, and that one class of homozygote females 
fails to achieve sexual maturity; hence, the frequency of adult males in 
a deme would reflect the local frequency of the A and B alleles and 
this, in turn, should agree with the ratio of adult females to males on 
the basis of the Hardy-Weinberg equilibrium. 
The hypothesis also accounts for a 1:1 sex ratio in stage V copepod- 
ites. Presumably, the polymorphism is adaptive in that the heter- 
ozygote female conserves both alleles and the local population benefits 
in having the ability to rapidly shift its genotype to meet crucial 
changes in local environmental conditions. In some aspects the avail- 
able data fit this model surprisingly well (table 9); however, the lack 
of concordance between adult and stage V morph frequencies and the 
overall sparseness of the data emphasize the need for more intensive 
collections representative of both range and seasonal fluctuations. 
Obviously, ultimate confirmation that genetic polymorphism is the 
basis for the observed facts will require breeding experiments. 
Relationship of the jollae Group to the Genus 
The three species described above are considered a species group, 
in the sense of Mayr (1963), as a consequence of sharing essential 
morphological similarities and occupying successive geographical 
